The device may be packaged separately from deployment tool and loaded with a stent in which the stent is then transferred into the deployment tool prior to placement. The deployment tool could be reusable. Also, the stent would not be subjected to compression set due to compression for prolonged period of time.
Self-expanding medical prostheses frequently referred to as stents are well known and commercially available. They are, for example, disclosed generally in the Wallsten U.S. Pat. No. 4,655,771, the Wallsten et al. U.S. Pat. No. 5,061,275 and in Hachtmann et al., U.S. Pat. No. 5,645,559. Stents are used within body vessels of humans for a variety of medical applications. Examples include intravascular stents for treating stenoses, stents for maintaining openings in the urinary, biliary, tracheobronchial, esophageal, and renal tracts, and vena cava filters.
The implantation of an intraluminal stent will preferably cause a generally reduced amount of acute and chronic trauma to the luminal wall while performing its function. A stent that applies a gentle radial force against the wall and that is compliant and flexible with lumen movements is preferred for use in diseased, weakened, or brittle lumens. The stent will preferably be capable of withstanding radially occlusive pressure from tumors, plaque, and luminal recoil and remodeling.
A delivery tool which retains the stent in its radially compressed state is often used to present the stent to a treatment site through tracts, lumens or vessels within the body. The flexible nature and reduced radius of the radially compressed stent enables delivery through relatively small and curved tracts, lumens or vessels. In percutaneous transluminal angioplasty, an implantable endoprosthesis is introduced through a small percutaneous puncture site, airway, or port and is passed through various body vessels to the treatment site. After the stent is positioned at the treatment site, the delivery tool is actuated to release the positioned stent. The stent is allowed to self-expand within the body vessel. The delivery tool is then removed from the patient. The stent remains in the vessel at the treatment site as an implant. Typically the delivery tool is designed for single use and so it is thrown away.
Stents must exhibit a relatively high degree of biocompatibility since they are implanted in the body. An endoprosthesis may be delivered into a body tract, vessel or lumen on or within a surgical delivery tool as shown in U.S. Pat. Nos. 4,954,126 and 5,026,377. Preferred delivery tools for the present invention may include modifications of those delivery tools so that there cooperate and interact with the present invention.
Commonly used materials for known stent filaments include Elgiloy and Phynox metal spring alloys. Other metallic materials than can be used for self-expanding stent filaments are 316 stainless steel, MP35N alloy, and superelastic Nitinol nickel--titanium. Another self expanding stent, available from Schneider (USA) Inc. of Minneapolis, Minn., has a radiopaque clad composite structure such as shown in U.S. Pat. No. 5,630,830 to Mayer. Self-expanding stents can be made of a Titanium Alloy. The strength and modulus of elasticity of the filaments forming the stents are also important characteristics. Elgiloy, Phynox, MP35N and stainless steel are all high strength and high modulus metals. Nitinol has relatively low strength and modulus but includes temperature dependent self expanding or superelastic properties that have benefits.
There is continued growth in procedures and applications of self-expanding stents with particular characteristics for use in various medical indications. Stents are needed for implantation in an ever increasing list of lumens and vessels throughout the patient's body. Different physiological environments are encountered and it is recognized that there is no universally acceptable set of stent characteristics.
High health care costs demand medical devices that can be sterilized and reused but heretofore stent delivery instruments were supplied by their manufacturers loaded with a stent and thus prepared for a single use and then disposal. That approach was acceptable for the introduction of stent vascular and lumenal surgery but was not cost effective. The need for equipment and techniques for loading stents into a delivery tool has not been addressed so that medical practitioners can do so in the preoperating room environment. Moreover the use of a sterilizable reusable delivery tool depends on an easy and effective loading device and fool proof method of use.